Eye benefits of vitamin A and beta-carotene

Does vitamin A do anything to help eyes and vision? Can a vitamin A
deficiency cause blindness? Is it dangerous to consume too much vitamin
A?

Read on for answers to these questions and other useful facts about this important antioxidant vitamin, including information about eye benefits of vitamin A and
beta-carotene, top vitamin A foods, and possible benefits of vitamin A
eye drops.

What Is Vitamin A?

Vitamin A actually is a
group of antioxidant compounds that play an important role in vision,
bone growth and health of the immune system. Vitamin A also helps the
surface of the eye, mucous membranes and skin be effective barriers to
bacteria and viruses, reducing the risk of eye infections, respiratory problems and other infectious diseases.

In general, there are two types of vitamin A, depending on the type of food source it comes from:

Sweet potatoes and carrots are excellent sources of provitamin A carotenoids that are good for your eyes.

Vitamin
A from animal-derived foods is called retinol. This "pre-formed"
vitamin A can be used directly by the body. Good food sources of retinol
vitamin A include beef and chicken liver, whole milk and cheese.

Vitamin A obtained from colorful fruits and vegetables is in the form of "provitamin A" carotenoids, which are converted to retinol by the body after the food is ingested. Good food sources of provitamin A carotenoids include carrots, sweet potatoes, spinach, kale and cantaloupes.

Beta-carotene is one of the most prevalent and effective provitamin A carotenoids.

Eye Benefits Of Vitamin A And Beta-Carotene

Because vitamin A helps protect the surface of the eye (cornea), it is essential for good vision.

Vitamin
A, at least when in combination with other antioxidant vitamins, also
appears to play a role in decreasing the risk of vision loss from macular degeneration
(AMD). In the landmark Age-Related Eye Disease Study (AREDS) sponsored
by the National Eye Institute, people with mild or moderate AMD who took
a daily multivitamin that included vitamin A (as beta-carotene), vitamin C, vitamin E, zinc and copper had a 25 percent reduced risk of advanced AMD during a six-year period.

It also appears that a combination of vitamin A and lutein may prolong vision in people suffering from retinitis pigmentosa
(RP). A four-year study conducted by researchers from Harvard Medical
School and other prominent universities found that individuals with
retinitis pigmentosa who took daily supplements of vitamin A (15,000 IU)
and lutein (12 mg) had a slower loss of peripheral vision than those who did not take the combined supplements.

Because
beta-carotene is converted into vitamin A in the body, it's likely this
provitamin A offers similar eye benefits as the pre-formed retinol type
of vitamin A, though more research is needed to confirm this.

And
researchers at Columbia University Medical Center found that a
synthetic, altered form of vitamin A might be able to slow the
progression of Stargardt's disease, an inherited eye disease that causes severe vision loss in young people.

When
given to mice with the same genetic defect as humans with Stargardt's
disease (also called juvenile macular degeneration), the modified
vitamin A inhibited the growth of clump-like deposits in the retina
called "vitamin A dimers" that are associated with degenerative changes
and vision loss.

The National Eye Institute has awarded the
researchers a $1.25 million grant to further investigate the link
between vitamin A dimers and various retinal degenerations, which could
lead to new approaches to treat these diseases.

Vitamin A Deficiency

Vitamin
A deficiency is rare in the United States, but it is common among the
poor in developing countries. It's estimated that approximately 250,000
to 500,000 malnourished children worldwide become blind each year due to
vitamin A deficiency that could have been prevented with a proper diet.

One
of the first signs of vitamin A deficiency is night blindness. In
ancient Egypt, it was discovered that night blindness could be cured by
eating liver, which later was found to be a rich source of vitamin A.

A lack of vitamin A causes the cornea to become very dry, leading to clouding of the front of the eye, corneal ulcers and vision loss. Vitamin A deficiency also causes damage to the retina, which also contributes to blindness.

Because
vitamin A also is important for resistance to infection and a healthy
immune system, vitamin A deficiency can lead to death from respiratory
and other infections.

Vitamin A - Daily Value

In most cases, it's best to obtain vitamins and minerals from a healthy, balanced diet.

The
concept of the Daily Value (DV) was developed to help consumers
determine if a food contains a lot or a little of a nutrient, based on
its Recommended Dietary Allowance. The DV for vitamin A is 5,000 IU.

The following tables provide DV percentages for some of the best vitamin A foods:

Vitamin A Toxicity

Vitamin
A that comes from animal food sources is not water-soluble and
therefore is not readily excreted from the body. Instead, it is stored
in body fat and, if ingested in excess amounts, can build up in the body
and become toxic.

Beta-carotene and other provitamin A
carotenoids found in fruits and vegetables don't pose the same vitamin A
toxicity risk. These compounds are water-soluble and are easily
eliminated from the body, so vitamin A toxicity from vegetarian food
sources is rare.

Beta-carotene supplements, however, may have
serious risks for smokers. Two studies have found that smokers taking
daily supplements containing 20 to 30 mg of beta-carotene had an
increased risk of lung cancer compared with smokers who did not take the
eye supplements.
(These studies are controversial, however, and a large study of more
than 22,000 male physicians found no adverse health effects when these
doctors took beta-carotene supplements of 50 mg every other day.)

The
Institute of Medicine has established the following upper intake levels
for the animal-based, retinol form of vitamin A to reduce the risk of
vitamin A toxicity:

Children (ages 4 to 8): 3,000 IU

Children (ages 9 to 13): 5,610 IU

Teenagers (ages 14 to 18): 9,240 IU

Adults (age 19 and older): 10,000 IU

Possible
toxicity reactions from long-term daily consumption of vitamin A above
these levels include birth defects, liver abnormalities, reduced bone
mineral density that can lead to osteoporosis, and central nervous
system disorders.

Eye Nutrition News

Breeding Sweet Potatoes In Africa To Fight Blindness

August
2015 — Sweet potatoes are a promising way to help vitamin A-deficient
children in South Africa, according to a June report in the journal Crop Science.
Vitamin A deficiency is the leading cause of preventable blindness in
children around the world. Sweet potatoes have naturally high amounts of
beta-carotene (which our bodies convert to vitamin A) and are already a
well-accepted food in South Africa.

"We realized it would be
great if we could develop a local variety which has good yield, high dry
mass, and desirable taste attributes, and promote it to combat vitamin A
deficiency," says Sunette Laurie, a senior researcher with the
Agricultural Research Council in Pretoria, South Africa.

Laurie
and others tested 12 varieties of sweet potatoes in humid subtropical,
drier subtropical and temperate climates. Impilo and Purple Sunset are
two varieties that have shown the best results. In a 4.4 ounce serving,
Impilo provides 113 percent of the daily vitamin A requirement of a
child 4 to 8 years old; Purple Sunset provides 261 percent. Another
variety called Bophelo has more beta-carotene than Impilo and tastes
better.

Laurie's team is working on more varieties with an eye
toward pest-resistance, and she is working toward the building of more
agro-processing units that would make flour, bread, muffins and other
foods from sweet potatoes.

Gary Heiting, OD, is senior editor of AllAboutVision.com. Dr. Heiting has more than 30 years of experience as an eye care provider, health educator and consultant to the eyewear industry. … read more

Columbia researchers work on preventing blindness from age-related macular degeneration and Stargardt's disease. Columbia University Medical Center. Press release. May 2011.
Clinical trial of lutein in patients with retinitis pigmentosa receiving vitamin A. Archives of Ophthalmology. April 2010.
National Nutrient Database for Standard Reference, Release 22. Agricultural Research Service, U.S. Department of Agriculture. December 2009.
A comparison of vitamin A and cyclosporine A 0.05% eye drops for treatment of dry eye syndrome. American Journal of Ophthalmology. February 2009.
Dietary Supplement Fact Sheet: Vitamin A and Carotenoids. Office of Dietary Supplements, National Institutes of Health. April 2006.
A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta-carotene, and zinc for age-related macular degeneration and vision loss: AREDS Report No. 8. Archives of Ophthalmology. October 2001.
Vitamin A eyedrops for superior limbic keratoconjunctivitis. American Journal of Ophthalmology. May 1988.